Yocto is operating system that can be use ini intel galileon or in intel edison. in linux yocto, you can write your code by use node js, python, etc. there are some reason for use linux yocto on your intel galileo or intel edison, like you need configure your controler like you use a PC from terminal,to autostart your app, you can configure your device to connect to internet.

Step 1: What You Need to Start?

Linux yocto image( you can download from http://downloadmirror.intel.com/24355/eng/SDCard.1...)
Memory card(sd card) with minmal capacity 4GB and max 32 GB. make sure your sd card is class 10.if you use lower than class 10(ke sd card class 6), maybe it make error when you install yocto to your sd card.
boot to usb aplication like rufus, win2usb or something like that

Step 2: Start Cook!!!

after you prepare your tools you need, first time you do format your sdcard to ntfs format. again make sure your sd card is class 10 or higher. from rufus you can create bootable by using ISO image that you downloaded before.

Step 3: Serve!!!

after you finish that process, you can check your sd card bootble. if your sd card contain file like show on the picture, it shows your sdcard ready to use. you can put your sd card into your intel galileo or intel edison